This year's work will focus on three fronts. Cell growth and DNA synthesis in the rat uterus may involve restriction points or arrest points that estrogen has to overcome. We will attempt to delineate the number and time course of these restriction points by a combination of estrogen treatments. We are also looking at details of DNA synthesis initiation and how it is controlled by estrogens. The second major area includes studies of the messenger RNA (mRNA) populations of uteri and the influence of estrogen on these populations. We hope to find evidence for a mRNA for the induced protein (IP) of the uterus. Estrogen receptors, the third area under study, will be looked at both in uterine and pituitary tissues. Cell cultures of pituitary tissue may provide the best system for studying the regulation of receptor concentrations.